[PATCH] ARM: bitops: Fix low-level code to be Thumb-2 compatible

[Nicolas Pitre]

On Wed, 2 Feb 2011, Dave Martin wrote:

> The new bitops code cunningly str <Rt>, [r1, -r1] to trigger
> a fault by attempting to store to address zero.
> 
> This code doesn't assemble in Thumb-2, since Thumb-2 doesn't
> allow negative register offsets at all for loads and stores.
> 
> The patch loads 0 into r2 and uses that as a base register
> instead for the Thumb-2 case: r2 seems non-live at every
> instance of this problem.
> 
> The ARM case is unaffected.
> 
> Signed-off-by: Dave Martin <dave.martin at linaro.org>

Russell proposed a better solution already:

http://mid.gmane.org/alpine.LFD.2.00.1101181312360.8580@xanadu.home

No idea why this wasn't folded in his series yet though.


Nicolas


> ---
>  arch/arm/lib/bitops.h |   16 ++++++++++++----
>  1 files changed, 12 insertions(+), 4 deletions(-)
> 
> diff --git a/arch/arm/lib/bitops.h b/arch/arm/lib/bitops.h
> index f8a2bd3..87d6b17 100644
> --- a/arch/arm/lib/bitops.h
> +++ b/arch/arm/lib/bitops.h
> @@ -1,7 +1,9 @@
>  #if __LINUX_ARM_ARCH__ >= 6
>  	.macro	bitop, instr
>  	tst	r1, #3
> -	strne	r1, [r1, -r1]		@ assert word-aligned
> + ARM(	strne	r1, [r1, -r1]	)	@ assert word-aligned
> + THUMB(	movne	r2, #0		)
> + THUMB(	strne	r1, [r2]	)
>  	mov	r2, #1
>  	and	r3, r0, #31		@ Get bit offset
>  	mov	r0, r0, lsr #5
> @@ -17,7 +19,9 @@
>  
>  	.macro	testop, instr, store
>  	tst	r1, #3
> -	strne	r1, [r1, -r1]		@ assert word-aligned
> + ARM(	strne	r1, [r1, -r1]	)	@ assert word-aligned
> + THUMB(	movne	r2, #0		)
> + THUMB(	strne	r1, [r2]	)
>  	mov	r2, #1
>  	and	r3, r0, #31		@ Get bit offset
>  	mov	r0, r0, lsr #5
> @@ -38,7 +42,9 @@
>  #else
>  	.macro	bitop, instr
>  	tst	r1, #3
> -	strne	r1, [r1, -r1]		@ assert word-aligned
> + ARM(	strne	r1, [r1, -r1]	)	@ assert word-aligned
> + THUMB(	movne	r2, #0		)
> + THUMB(	strne	r1, [r2]	)
>  	and	r2, r0, #31
>  	mov	r0, r0, lsr #5
>  	mov	r3, #1
> @@ -61,7 +67,9 @@
>   */
>  	.macro	testop, instr, store
>  	tst	r1, #3
> -	strne	r1, [r1, -r1]		@ assert word-aligned
> + ARM(	strne	r1, [r1, -r1]	)	@ assert word-aligned
> + THUMB(	movne	r2, #0		)
> + THUMB(	strne	r1, [r2]	)
>  	and	r3, r0, #31
>  	mov	r0, r0, lsr #5
>  	save_and_disable_irqs ip
> -- 
> 1.7.1
> 
> 
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